The present invention relates to a method for operating a hybrid drive of a vehicle and, in particular, to a method for operating a hybrid drive and that can be operated at least selectively in a first operating mode powered by only an internal combustion engine or in a second operating mode powered by only an electric motor.
DE 10 2006 033 930 A1 of Robert Bosch GmbH discloses a method for operating a hybrid drive of a vehicle. According to this method, a travel profile is determined for a route that is to be traveled; and then the internal combustion engine and the electric motor of the hybrid drive are controlled as a function of the operating parameters obtained from determining the travel profile. The “travel profile” can be the result of a number of different parameters, such as the length of the route, the altitude profile, location of intersections and/or traffic lights, road class, etc. Moreover, the parameters can be set manually by way of a navigation system. It is stated explicitly that the operating strategy is selected with respect to at least one of the following criteria: the fuel consumption, the emission of pollutants, the state of charge and/or the service life of the electrical storage device. It is not, however, apparent just how “predictive” the method described in DE 10 2006 033 930 A1 may be.
In many of the known operating strategies for hybrid vehicles the “control horizon” is very limited. In some operating strategies this control is even purely situational, i.e. based solely on the parameters of the momentary driving conditions or, more specifically, on the momentary system parameters.
The object of the present invention is to provide a method that is designed for operating a hybrid drive and with which it is possible to obtain an even better optimum use of the use of the drive energy (in the form of fuel and electrical energy) available in the vehicle.
This and other objects are achieved by a method for operating a hybrid drive, which can be operated at least selectively in a first operating mode powered by only an internal combustion engine or in a second operating mode powered by only an electric motor. Prior to the start of a trip, for which a route that leads from a start to a destination is determined, the entire route to be traveled is divided, according to a pre-defined logic, into a plurality of route sections. These route sections are used to select those route sections that are ever taken into consideration at all, based on certain route section criteria, for driving in the second operating mode. These selected route sections, in turn, are used to identify and to drive on the route in the second operating mode, in which travel on the route in the second operating mode yields in total an advantage in terms of maximum fuel economy as compared to driving on the route in the first operating mode or in any other operating mode.
The invention recognizes that a hybrid operating strategy that is designed for the current operating point of the vehicle provides only a suboptimum result. It has been recognized that the control horizon of the operating strategy has to be significantly extended in order to make optimum use of the energy, even in the case of longer trips, for which an entire tank of fuel or more fuel may be consumed.
A fundamental aspect of the invention consists of the description of the underlying object as a “reverse backpack problem.” In practical terms, the issue is that the driver of a hybrid vehicle, in particular a so-called “plug-in hybrid,” would like to charge the electrical energy storage device, which may be found in the vehicle, and would like to use the electrical energy stored in the vehicle for an “electric driving mode” in such a way that he saves the maximum amount of fuel that is used to drive the internal combustion engine of the vehicle. This problem raises the question: on which route sections of a given route should he travel, preferably using the electric drive of the vehicle. Thereafter, the operating strategy of the invention determines which operating mode should the vehicle be driven in, i.e., in a first operating mode powered by an internal combustion engine or in a second operating mode powered by only an electric motor and/or in a third operating mode (for example, combined internal combustion engine and electric motor powered operation).
According to the invention, prior to beginning a trip, the route between a starting point and a destination point is divided, according to a pre-defined logic, into a plurality of route sections. Then, from these route sections are (pre)selected those route sections that are ever taken into consideration at all, based on certain route section criteria, for driving in the second operating mode, i.e. for driving the route sections in an operation powered by only an electric motor. These selected route sections, in turn, are used to identify and then to drive in the second operating mode, a route in which travel on the route in the second operating mode yields in total an advantage in terms of maximum fuel economy as compared to driving on the route in the first operating mode or in any other operating mode.
As stated above, the control horizon covers an arbitrarily long route to be traveled. In other words, the entire route to be traveled is always analyzed independently of the length of the route to be traveled. That is, the entire route to be traveled is broken down into individual sections of the route. Then, the individual route sections are used to select those sections of the route that may be considered for driving in the second operating mode. These selected route sections are then used to identify those route sections, which would yield in total an advantage in terms of maximum fuel economy if they were driven in the second operating mode as compared to being driven in the first operating mode or in any other operating mode.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.